Delay performances of a continuous arq system with copy-transmissions

The characteristics of packet transmission delay in a continuous ARQ (Go-Back-N type) system are analyzed here. The copies of each packet stored in the buffer are sent to reduce the delay. The optimum copy size minimizing the delay depends not only on packet error probability and round-trip propagation delay but also on offered traffic intensity. It is possible to reduce the delay by transmitting many copies and using the residual transmission capacity when offered traffic is light. On the contrary, when offered traffic is heavy, transmission of few copies is preferable in consideration of the number of lost copies for a successful transmission. Finally, considering that packet error probability may be reduced in some practical situations, the relation among packet error probability, propagation delay and traffic density where the optimum copy size changes from 1 to 2 is derived.